Production of low sulfate uranium oxide



7 Andrew Kelrners, Warwick,"N.Y., :assignor to Union Carbide Corporation, a corporation of' New York No Drawing. Filed Apr. 1960, Ser. No. 22,408 i 2 Claims. .(Cl. 23- 145) This invention relates to "the production of oxidic uranium concentrates and specifically to the'production, of sulfate'free. oxidic uranium concentrates bysolven extraction methods.

Western States. v tain uranium oxide in greater than 1.0 percent and usually contain uranium oxide in about 0.1-03 percent. In addition, the fissionable specie of uranium constitutes only about 0.7 percent of all the uranium present in the ore. Since large amounts of ore must be treated to acquirethelinal uranium in any significant amount, it is imperative that extensive concentration steps be carried out in the vicinity of the mines to produceiur'anium concentrates therebyreducing the burden of shipping excess ganguewith the values. p l I u a 1 W The metallurgical art surrounding uranium 'r'el-ies heavi 6 Uni saes Patent o p byadjusting the pH of the secondary liquorby adding H SO and'eliminating the carbonate componentof the uranyltrioarbonate -'-b'y heating The pH is adjusted to' 'approximately '2 by the addition of sulfuric acid. Proondary' liquor is a batchwise process and is facilitated.

cipitation. is initiated and completed by addition of: gase ous ammonia until the pH of the secondary liquor is approximately .to '8; The; uranium values precipitate from the basicjsol ution which has'been purged of its carbonate component. 1

- Theprior art teaches the necessity of prolonging the u I length of'the precipitation step'andthe thickening and Uranium occurs as various minerals throughout the The uranium bearing. oren rarely .con-

filtration steps to enable a greater contact time between the uranium oxide precipitate and the-secondary liquor 'Which contains the uranium values in solution. Afterthelong digestion period the precipitate is thickened;

filtered, washed in'an attempt to decrease the sulfate content and calcined toa final, oxidic uranium product. i

e final product is commonly referred, to as .yellow cake.

A period of several hours or even days will elapse in the prior art batch process of thickening and filtering-before'the'precipita'ted .uranium values are separated from lly -on the solvent-extraction process-of concentrating;

uranium oxide from the mother ore s. 1 This process has prov-ed exceedingly satisfactory in separating uranium oxide values from the parent ore butin some' respects and in some adaptations of solvent-extraction aproblem of detrimental sulfate contaminationihas' arisen. This leads to a final concentratewith sulfate contamination as .high as 12-17 percent by Weight of the final unanium oxide concentrate. Penalties are levied by the Atomic Energy Commission in commercial transactions based upon the sulphate level in the products. I

Throughout this specification, solutions containing the uraniunrvalues will be termed liquors. Solutions" sub 'stantially free of uranium values will be termed simply v.bar'ren solutions. a In addition, the term ogddic uranium will be'construed and used herein to :indicate'all derive.

tionto e t'racteoxidic uranium by 1 fa m a s di r l hat a h q nt phase. The uraniu'm loadedjsolvent-extractant phase isseparated "fromthe now .barr en'lea'cli solution and stripped of the uranium values by causing the loaded eXtracta-nt phase to contact a basic sodium-carbonate solution. The carbonate component in the basic sodium carbonate stripping solution causes the effiuent uranium valuesto stay in solution as sodium uranyltricarbonate. Thestripping solution is thereby rendered the carrier of. the uranium values as a sodium-carbonate secondary liquor. The recovery of uranium values fronithesec-i I duce the'oigidicuranium precipitate which' is formedibyf thefadez.

ditionjfof gaseous ammonialto these 'ond s q 'I'hisfis directly in opposition to priori teachingsnwhich advocated thenecessity'of'a-n. increased-ingestion time] Though the problem .of sulphate contamination has? the sulphate-containing secondary liquor. The yellow cake produced by ,the aforementioned prior art method is characterized by ahigh residual sulphate contentnormall'ygrunning inthe range of fi'om-l2- l7 Weight percent sulphate. j gResidual sulphate jin the? yellow cake vis considered deleterious later beneficiation and purification steps as evidenced by the present j penalties whichhave been established bythe 'A.E.C-.';on"yellow cake concern;

trates containing-greater than l0;per cent-of the total weight of uranium oxide componentpas a sulphatecom-g ponent. I

Theobject of the present invention ism putforth process-for the production of oxidic uranium wherein the extent of deleterious residual sulphate'contamination' is controlled and a filterable oxidic uraniumprecipitate is obtained.

.It is another object of the present process to-iproduce oxidic uranium which does not contain greater than 10 I i weight percent 'sulphate in the fi naltproduct f jIt is furtheran object of thefpresent .processto ;pr,o- W ridic uranium having ;less\ than; '1 Weight; percent res d l u bh t s nt mi iqn.

.Ot ers icc s -w ll @pparentifrom; the reinainin (ll existed for quite some time, no satisfact'ory solution has been found; The relationshipdof contacttimejbetween the oxidic uranium precipitate and the sulphate-containing secondary liquor and the effect of'the extent of contact time of contact between thesecondaryd1duor. and: I

The inventor has found that as the secondary solution is neutralized with ammonia, the bulk of the uranium values precipitate as hydrated oxides of uranium similar in composition and structure to the mineral becquerelite. This is the desired sulphate free precipitate. If this precipitate is allowed to stay in contact with the sulphate containing secondary liquor in either the precipitation or the filtration steps for an extended length of time, the becquerelite transforms into a basic uranyl sulphate which is analogous to the mineral zippcite. After this transformation, the sulphate cannot be washed from the zippeite mineral and as a consequence the fin al uranium oxide produut contains high sulphate.

The present invention employs a decrease in the contact-time while still maintaining the production of a filterable product. From the physical set up of the process of oxidic-uranium extraction by the aforementioned prior art method there are three steps during which the concept of the present invention can be applied. They are during precipitation, thickening and/or filtration. Since it is conceivable that all can, and in many instances are, conducted simultaneously in a single batch operation or in a continuous operation, the inventor will not limit the application of their improvement to any particular step of the process of precipitation and separation of the uranium oxide product. Rather the inventor teaches a substantial decrease in the contact time between the uranium oxide precipitate and the sulfate secondary liquor. Such a decrease can be effected by modifying the rate of precipitation, thickening and/or filtering time singly or in combination in such a manner as to decrease the total contact time to less than approximately 1 hour.

Tests to ascertain the relationship between contact time and sulphate analysis in the final product have been carried out as follows: I

A slow precipitation of 4.75 hours was conducted on a standard secondary liquor by the introduction of gaseous ammonia followed by rapid thickening and filtration. The resulting yellow cake contained 9.7 weight percent sulphate. Rapid precipitation was then conducted on a standard secondary liquor followed by slow thickening and filtering. The resulting yellow cake analyzed 14 to 17 Weight percent sulfate. The tests show that the combined time for precipitation and filtration, including thickening, controls the sulfate contamination in the product.

The following examples will further illustrate the present invention:

A large batch of acidified secondary liquor at pH 2.9 was precipitated by recycling the solution and adding ammonia at the recycle pump until a final pH of 7.2 was reached. Two hours and ten minutes time was expended to complete the ammonia addition. The uranium started precipitating at a pH of about 5. The actual time in which solid precipitate was in contact with mother liquor was less than two hours. Samples were collected during rand-immediately following'precipitation. They were filtered and washed immediately. Samples of oxidic uranium taken during the precipitation showcdsulfate' contents of 0.64 to 1.8 weight percent.

' Threesamples were taken from the tank immediately after the precipitation was completed (less than 2 hours contact time) and these samples showed that the sulfate ranged from 0.70 to 1.0 weight percent. The remaining 'batch of precipitate was then processed by prior art thickening and filtration procedure. The solids contained 14 to 17 weight percent sulfate after such thickening and filtering thereby demonstrating the necessity of rapidy filtering the solids.

In order to. obtain a better estimation of the maximum time limit for the precipitation and filtration steps, additional work was carried out. A sample of secondary sulfate strip solution was acidified with sulfuric acid and boiled to destroy the carbonate. This solution contained, by analysis, 71.8 g./l. of U 0 and 110 g./l. of sulfate. Portions of it were precipitated by adding concentrated ammonium hydroxide over the periods of time indicated in Table I. The solids were promptly filtered and washed with water.

Precipitation time (minutes): Sulphate analyses,

The results of the test as shown in Table I indicate that up to minutes could be allowed for the precipitation and filtration steps while still maintaining 1 weight percent or less of sulfate contamination.

It is readily seen from the above description and examples that the contact time between the oxidic uranium precipitate and the secondary sulfate liquor is all controlling of the final sulphate analysis in the final product. It is not deemed necessary to recite the numerous routine mechanical variations which a person skilled in the pertinent art would readily employto adapt the present invention to the many specific situations in which this invention is amenable.

What is claimed is:

1. In the proces of producing oxides of uranium from uranium ore comprising leaching uranium values from 'ore to form a pregnant leach liquor, contacting said leach liquor with a solvent extractant to transfer said uranium values from said pregnant leach liquor to said solvent extractant thereby forming a loaded solvent extractant, removing said loaded solvent extractant from contact with said leach liquor, contacting said loaded solvent extractant with a sodium carbonate stripping solution thereby causing the uranium values to transfer from said loaded solvent extractant to said sodium carbonate stripping solution to form a sodium carbonate secondary liquor, adding sulfuric acid to said sodium carbonate secondary liquor until said sodium carbonate secondary liquor is converted to an acidic secondary sulphate liquor having a pH of about 2, heating said acidic secondary sulphate liquor to a temperature sufficient to decompose the carbonate component and maintaining said temperature until said carbonate component is substantially decomposed, and adding an ammonia compound to said acidic secondary sulphate liquor until said acidic secondary sulphate liquor has been converted to a basic secondary sulphate liquor having a pH of about 7 to 8 and thereby causing precipitation of the uranium values from the basic secondary sulphate liquor as an oxidic uranium precipitate, the improvement comprising removing said precipitate from said basic secondary sulphate liquor before said precipitate has been in contact with said basic secondary sulphate liquor for a I period of greater than about 1 hour; and washing said precipitate to form a final oxide of uranium containing less than about 1.0 weight percent sulphate.

2. In the process of producing oxides of uranium from uranium ore comprising leaching uranium values from ore to form pregnant leach liquor, contacting said leach liquor with'a solvent, extractant to transfer said uranium values from said pregnant leach liquor to said solvent extractant thereby forming a loaded solvent extractant, removing said loaded solvent extractant from contact with said leach liquor, contacting said loaded solvent extractant with a sodium carbonate stripping solution thereby causing the uranium values to transfer from said loaded solvent extractant to said sodium carbonate stripping solution to form a sodium carbonate secondary liquor, adding sulfuric acid to said sodium carbonate secondary liquor until said sodium carbonate secondary liquor is converted to an acidic secondary sulphate liquor having a pH of about 2, heating said acidic secondary sulphate liquor to a temperature sufiicient to decompose the carbonate component "and maintaining said temperature until said carbonate component is substantially decomposed, and adding an ammonia compound to said acidic secondary sulphate liquor until said acidic secondary sulphate liquor has been converted to a basic secondary sulphate liquor having a pH of about 7 to 8 and thereby causing precipitation of the uranium values from the basic secondary sulphate liquor as an oxidic uranium precipitate, the movement comprising removing said precipitate fnom said basic secondary sulphate liquor before said precipitate has been in contact with said basic secondary sulphate liquor for a period of greater than about :15 hour; and washing said precipitate to form a final oxide of uranium containing less than about .25 weight percent sulphate.

References Cited in the file of this patent UNITED STATES PATENTS Stamberg Oct. 17, 1939 Brimrn Jan. 2, 1951 Nye et a1. Oct. 6, 1953 Karnen et a1. Sept. 4, 1956 Brundin Sept. 11, 1956 Spiegler Nov. 20, 1956 Ballard Jan. 29, 1957 Kimball et al July 23, 1957 King et a1 2- Aug. 12, 1958 Brown Mar. 10, 1959 'UNITED STATES PATENT UFFICE CERTIFICATE OF CORRECTION Patent No. 3, 100,682 August 13, 1963 Andrew D. Kelrners It is hereby certified that error appears in the above numbered patent reqiiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 8, for "movement" read improvement Signed and sealed this 14th day of April 1964.

(SEAL) Attest: EDWARD J. BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents 

1. IN THE PROCESS OF PRODUCING OXIDES OF URANIUM FROM URANIUM ORE COMPRISING LEACHING URANIUM VALUES FROM ORE TO FORM A PREGNANT LEACH LIQUOR, CONTACTING SAID LEACH LIQUOR WITH A SOLVENT EXTRACTANT TO TRANSFER SAID URANIUM VALUES FROM SAID PREGNANT LEACH LIQUOR TO SAID SOLVENT EXTRACTANT THEREBY FORMING A LOADED SOLVENT EXTRACTANT, REMOVING SAID LOADED SOLVENT EXTRACTANT FROM CONTACT WITH SAID LEACH LIQUOR, CONTACTING SAID LOADED SOLVENT EXTRACTANT, WITH A SODIUM CARBONATE STRIPPING SOLUTION THEREBY CAUSING THE URANIUM VALUES TO TRANSFER FROM SAID LOADED SOLVENT EXTRACTANT TO SAID SOLVENT SODIUM CARBONATE STRIPPING SOLUTION TO FORM A SODIUM CARBONATE SECONDARY LIQUOR, ADDING SULFURIC ACID TO SAID SODIUM CARBONATE SECONDARY LIQUOR UNTIL SAID SODIUM CARBONATE SECONDARY LIQUOR IS CONVERTED TO AN ACIDIC SECONDARY SULPHATE LIQUOR HAVING A PH OF ABOUT 2, HEATING SAID ACIDIC SECONDARY SULPHATE LIQUOR TO A TEMPERATURE SUFFICIENT TO DECOMPOSE THE CARBONATE COMPONENT AND MAINTAINING SAID TEMPERATURE UNTIL SAID CARBONATE COMPONENT IS SUBSTANTIALLY DECOMPOSED, AND ADDING AN AMMONIA COMPOUND TO SAID ACIDIC SECONDARY SULPHATE LIQUOR UNTIL SAID ACIDIC SECONDARY SULPHATE LIQUOR HAVING A CONVERTED TO A BASIC SECONDARY SULPHATE LIQUOR HAVING A PH OF ABOUT 7 TO 8 AND THEREBY CAUSING PRECITATION OF THE URANIUM VALUES FROM THE BASIC SECONDARY SULPHATE LIQUOR AS AN OXIDIC URANIUM PRECIPITATE, THE IMPROVEMENT COMPRISING REMOVING SAID PRECIIPITATE FROM SAID BASIC SECONDARY SULPHATE LIQUOR BEFORE SAID PRECIPITATE HAS BEEN IN CONTACT WITH SAID BASIC SECONDARY SULPHATE LIQUOR FOR A PERIOD OF GREATER THAN ABOUT 1 HOUR; AND WASHING SAID PRECIPITATE TO FORM A FINAL OXIDE OF URANIUM CONTAINING LESS THAN ABOUT 1.0 WEIGHT PERCENT SULPHATE. 